Why when the brush Yoke on an a.c. motor is moved to the reverse position it won't run

Why when the brush yoke on an a.c. motor is moved to the reverse position it won't run

Do you mean removing the brush turning it 180degrees and putting it back in? Electric motors are finicky about about their brushes if worn out you should just get new brushes and clean rotor where brush contact is made with a pencil eraser.hope that answered you question please rate my answer thanks:)